In education the saying is if you like content teach high school, if you like kids teach the young kids. I don't think this is true. Nothing is a replacement for being more of an expert in your field. I have a teaching certificate in high school math, which means that I have the equivalent of a Bachelor's degree in Mathematics.
Research shows that younger students attitudes in mathematics are directly correlated with the implicit attitudes of their teachers. For example, a 5th grade teacher who does not particularly enjoy math but still can teach math at a 5th grade level, his/her attitudes can implicitly impact your child. This impact is even greater for young girls with female teachers.
Over the years I have spoken with many people about their relationship to math, and once they find out that Mathematics is my passion, most people will say, "Better you than me, I hated math..." and then they continue to tell me the teacher that they had the year they stopped liking it. I think this is very telling.
The sooner you get your child help when they are falling behind in math, the better it is for them, now and for their future in mathematics.